DESCRIPTION (Verbatim from the applicant's abstract): The goal of this proposal is to understand the signaling mechanisms and the cellular responses of the control C. elegans sperm differentiation. Studying a simple experimental system that can be manipulated genetically, and analyzed on a genomic scale, facilitates discovery of the molecular mechanisms controlling cellular differentiation that will be applicable to other organisms including humans. Our studies of the activation of spherical spermatids to form asymmetric crawling spermatozoa has identified seven genes that participate in this process. We have selected another 20 candidate genes based on our studies of gene expression by DNA microarray analysis, which has identified many new sperm-specific genes. We will refine a working model of the sperm activation pathway by studying both the signaling process and the cellular responses. This will include analysis of sperm activation signaling by determining the subcelluar location of the known proteins and how they interact to control cellular physiology, particularly for the SPE-6 kinase, which controls MSP assembly and sperm activation. We will examine the cellular responses of the spermatid to the activations signaling pathway by studying the role of [Ca++] and pH changes in initiating MSP assembly, pseudopod formation, membranous organelle fusion and cellular motility. The putative calcium channel, SPE-39, regulates these processes, so we will determine its role. To identify physical interactions between the proteins involved in the sperm activation pathway, we will examine their interactions with the yeast two-hybrid system and apply physiology, biochemistry and genomics, will lead to a more complete molecular understanding of the processes underlying cellular differentiation. This will contribute directly to understanding human diseases because genes in this pathway are homologues to human disease genes.